P08.17.A DELIVERY OF AN ONCOLYTIC HSV-1 VIRUS THROUGH CARRIER MONOCYTES IN A MICROFLUIDIC BLOOD-BRAIN-BARRIER MODEL

Abstract BACKGROUND Oncolytic viruses (OVs) that replicate selectively in cancer cells are a promising approach for the treatment of glioblastoma (GBM), the most common primary brain tumor in adults and one of the deadliest solid tumors. However, delivering OVs to the central nervous system (CNS) remains a challenge. Intracranial injection cannot be easily repeated and could fail to infect the entire tumor, while intravenously injected therapeutics must cross the blood brain barrier (BBB). We previously demonstrated that both continuous and primary human monocytes (PHM) could transfer oHSV1 to cancer cells in vitro and validated their trafficking towards tumors in the vasculature of the chicken embryo chorioallantoic membrane (CAM) model. Here we report a human, in vitro microfluidic BBB model featuring primary astrocytes, pericytes and endothelial cells and its use to evaluate the potential of monocytes infected by oHSV1 to migrate toward GBM spheroids and to transmit them the infection. MATERIAL AND METHODS The microfluidic device was molded in polydimethylsiloxane (PDMS) using soft lithography techniques with an apical and a basolateral compartment, separated by a transparent polyester membrane with 3µm pores. Human umbilical vein endothelial cells were seeded on the apical side of the membrane, while astrocytes and pericytes were seeded on the basolateral side. GBM spheroids were produced culturing U87-MG cells in ultra-low attachment (ULA) plates and moved to wells in the basolateral compartment of the device. Monocytes were infected with a neuroattenuated oncolytic herpes simplex virus type 1 (oHSV1) expressing mCherry, generated with a bacterial artificial chromosome (BAC) mutagenesis technique and perfused into the blood-side inlet of the microfluidic device. Fluorescence and confocal microscopy was used to monitor the migration of monocytes labeled with a green fluorescent tracker and infection of the spheroids, marked by red fluorescence. RESULTS We showed that our model mimics the BBB physiological function in terms of permeability to dextran solutions and electrical resistance. Both PHM and THP-1 monocytes infected with oHSV1-mCherry crossed the BBB in the microfluidic system, toward GBM spheroids. Monocytes could transmit the infection to spheroids causing loss of structural integrity and viability. Carrier cells infiltrated tumoral spheroids leading to an “inside-out” pattern of viral diffusion, opposite to what is observed with cell-free virus. Importantly, monocytes protected oHSV1 from neutralizing antibodies in the microfluidic circuit, allowing infection of GBM spheroids, while free virions were neutralized. CONCLUSION Using an advanced in vitro BBB model, we show that monocytes can act as carrier cells for therapeutic HSV-1 vectors in the CNS, paving the way for the intravenous delivery of oHSV1 to brain tumors.